Availability of nitrogen in 15N-labeled ruminant manure components to successively grown crops

To improve crop N use efficiency of animal manures, the availability of N in individual manure components must be better understood. This microplot field study quantifies crop offtakes of N in four similar batches of ruminant manure containing N-15-labeled urine, feces, or straw, or unlabeled components only. The urine and feces were from a sheep first fed unlabeled hay and then N-15-labeled hay. Manures (approximate to 19 g total N m(-2)) were incorporated into two coarse-textured soils before planting to spring barley (Hordeum vulgare L.) undersown with perennial ryegrass (Lolium perenne L.), Manures with one N-15-labeled component were supplemented with unlabeled NH4NO3 (7.3 g N m(-2)), while unlabeled manure was given (NH4NO3)-N-15-N-15. Labeled and unlabeled N were determined in the spring barley at maturity and in six cuts of ryegrass taken during the succeeding 2.5 Sr, The homogeneity of feces and urine N-15-labeling was high. Dry matter yields and crop N offtakes were similar in all treatments. Barley (grain and straw) recovered 40, 26, 10, and 6%, respectively of N-15 added with mineral fertilizer, urine, straw, and feces. Weighted mean recovery of the combined manure and fertilizer dressing was 22% of the added N-15. Crop recovery of urine and feces N-15 was smaller and that of straw N-15 higher than reported in previous studies on individual components, indicating that the N mineralization-immobilization turnover (MIT) of the manure components interacted. In the second and third growth seasons, 2.7 to 4.4% and 1.1 to 2.0% of the N-15 was recovered in grass cuts, respectively, Total recovery ranged from 84 to 95% of the added N-15, suggesting small N losses from this cropping system.